Load-adaptive control system, in particular for transport devices and used in aircraft

ABSTRACT

The invention relates to a monitoring unit ( 5 ) for monitoring a first control value (I nom ) for overshooting or undershooting of a threshold value (I max ) with the first control value (I nom ) being used for controlling an apparatus ( 3 ). The monitoring unit ( 5 ) in this case has determination means ( 10, 20, 30, 40, 45 ) for determining the threshold value (I max ) from an instantaneous value (I s ) of the first control value (I nom ) when the apparatus ( 3 ) reaches a predetermined operating state, and monitoring means ( 50, 60 ) for monitoring the first control value (I nom ) for overshooting or undershooting of the determined threshold value (I max ) after the apparatus ( 3 ) has reached the predetermined operating state.

CROSS-REFERENCE TO RELATED APPLICATION

The instant application is a divisional application of U.S. patentapplication Ser. No. 09/943,328 filed Aug. 29, 2001 now U.S. Pat. No.6,662,075.

BACKGROUND OF THE INVENTION

The present invention relates to a control system, in particular fortransport devices as used in aircraft.

Conveyor belts without closed-loop control are generally used forloading aircraft and initially have items of cargo placed on them,across their width, while they are stationary. Typically, once theentire width of the conveyor belt has been completely filled, theconveyor belt is moved onward, so that the load located on the conveyorbelt is moved further to the rear into the aircraft.

In loading systems such as these, the loading process is thus brokendown into two repeatedly recurring steps, namely a first loading step,in which the load is placed on the belt while it is stationary, and asecond conveying step, in which the loaded belt is moved onward. Theaircraft can in this way be filled layer by layer by the repeatedsequence. Since the total load is increased with each loading step, theload being conveyed also increases in a corresponding manner with eachconveying step.

Typically, the first loading steps present no problems for the entireloading process since in this case, firstly, there is still little loadto be moved and, secondly, the load is also generally still largelylocated in the field of view of the load handler. Any sliding of theload, possibly resulting in the conveyor belt being blocked to a greateror lesser extent, can in general still be identified well during thesefirst loading steps. Furthermore, the power of the motor driving theconveyor belt is typically also dimensioned such that, when the conveyorbelt is only partially loaded, slight jamming or sliding of the loaddoes not yet actually lead to the conveyor belt becoming totallyblocked.

However, it can readily be seen that, as the loading process increases,and the load to be moved as well as the distance of the load from thepoint where the load is placed on the belt increase, the probability offaults rises, for example due to individual items of cargo sliding orbecoming jammed. This can lead to the conveyor belt becoming completelyblocked even before it has been completely filled which, particularly intime-critical situations such as when loading and unloading aircraft,can lead to undesirable and possibly costly time delays before the faultis identified and has been rectified. Furthermore, the blocking ofindividual items of cargo, even when this does not lead to a totalblockage, can lead to power surges, which last for greater or lessertimes, on the conveyor belt motor, which can in turn shorten themaintenance intervals for the conveyor system, and can reduce its life,in the long term.

While three-phase motors without closed-loop control are generally usedat the moment for conveyor belt systems for loading aircraft, FIG. 1shows a servo drive system with closed-loop control. A regulator 1receives, as input variables, a nominal rotation speed N_(nom) and ameasured actual rotation speed N. The regulator 1 uses the differencebetween the actual rotation speed N and the nominal rotation speedN_(nom) to define a current value I_(nom) which corresponds essentiallyto a torque level that is to be set. The regulator 1 passes the currentvalue I_(nom) to an amplifier 2, which in turn acts on an actuator (ormotor) 3. The actuator 3 operates a load 4. The actual rotation speed Nis measured at the actuator 3, and is fed back to the regulator 1.

The servo drive system with closed-loop control shown in FIG. 1, incontrast to the drive system without closed-loop control, allows thetorque of the actuator 3 to be readjusted if its rotation speed N doesnot match the nominal rotation speed N_(nom). However, this arrangementhas the problem of surges in the load 4, which, if there is adiscrepancy between the actual rotation speed N and the nominal rotationspeed N_(nom), can lead to the power of the actuator 3 being increased,and can thus possibly excessively overload it.

Furthermore, malfunctions, for example due to blocking or jamming ofitems of cargo, are not identified and can thus further increase theload on the actuator 3.

The present invention is based on the object of providing an improvedloading device which can also be used in particular for loadingaircraft.

SUMMARY OF THE INVENTION

The present invention provides a monitoring unit for monitoring a firstcontrol value for overshooting or undershooting of a threshold value,which is used for controlling an apparatus. The monitoring unit in thiscase has determination means for determining the threshold value from aninstantaneous value of the first control value when the apparatusreaches a predetermined operating state. Furthermore; the monitoringunit has monitoring means for monitoring the first control value forovershooting or undershooting of the determined threshold value afterthe apparatus has reached the predetermined operating state.

By determining the threshold value from the instantaneous value of thefirst control value when the apparatus reaches the predeterminedoperating state, the monitoring unit can carry out adaptive monitoringof the first control value, in each case matched to the conditions whichalso actually occur on reaching the predetermined operating state.

In one preferred embodiment, the determination means has a firstidentification means for monitoring an operating parameter of theapparatus for identification of the predetermined operating state of theapparatus. The identification means in this case uses the behavior ofthe operating parameter to deduce that the apparatus has reached thepredetermined operating state.

The first identification means preferably has a comparator for comparinga predetermined value of the operating parameter with a modeled value ofthe operating parameter, in which case, if the values match, it isdeduced that the apparatus has reached the predetermined operatingstate. The modeling of the values for the operating parameter in thiscase makes it possible to define and vary the reaching of thepredetermined operating state irrespective of the actual conditions.This makes it possible, in particular, to reduce the influence oftransient processes (for example with an overshoot and/or undershoot),which could incorrectly indicate that the predetermined operating statehad been reached.

As an alternative to the model value, the comparator can also comparethe predetermined value of the operating parameter with an actual valueof the operating parameter. This makes it possible to define thereaching of the predetermined operating state as a function of theactual conditions.

The instantaneous value at the time when the predetermined operatingstate is reached is preferably stored. This stored value then representsthe initial value for further monitoring of the first control value.

In a further embodiment, the determination means has a definition meansfor defining the threshold value from the instantaneous value of thefirst control value when the apparatus reaches the predeterminedoperating state, and from a permissible discrepancy. In this case, thepermissible discrepancy may, for example, be a fixed value or may alsobe adaptively matched to the given conditions.

The monitoring means preferably has a second identification means foridentifying whether the first control value is greater than or less thanthe determined threshold value.

The monitoring means preferably has a third identification means foridentifying whether the first control value is greater than or less thanthe determined threshold value and whether the apparatus is in thepredetermined operating state. In this way, the monitoring forovershooting or undershooting of the determined threshold value can berestricted to the time period after the apparatus has reached thepredetermined operating state. A warning signal for the apparatus ispreferably set when the determined threshold value is overshot orundershot.

The monitoring unit according to the invention is preferably used for acontrol system, for example for an actuator. The control system can inthis case be used in particular for such transport devices, for examplethose in an aircraft, in which loading initially takes place in astationary condition and the load is then transported further, as wasdescribed initially.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages, features and details of the invention will becomeevident from the following description of preferred exemplaryembodiments and from the drawings, in which:

FIG. 1 shows a known servo drive system with closed loop control;

FIG. 2 shows a preferred embodiment according to the present invention;

FIG. 3 shows a preferred exemplary embodiment of the decision-maker 5from FIG. 2 in the form of a block diagram; and

FIGS. 4 and 5 show an illustration of the method of operation of thedecision-maker 5 with various loads.

DETAILED DESCRIPTION

FIG. 2 shows one preferred embodiment of the present invention for theexample of a control system for a transport device, in particular inaircraft. In a corresponding way to the illustration in FIG. 1, thecontrol system shown in FIG. 2 has the regulator 1, the amplifier 2 andthe actuator 3, which in turn operates the load 4. The regulator 1receives, as input variables, the nominal rotation speed N_(nom) and theactual rotation speed N, and uses them to determine a control value forcontrolling the actuator 3. As the output from the regulator 1, thiscontrol value is preferably the current value I_(nom), which is suppliedvia the amplifier 2 to the actuator 3, and which essentially correspondsto the torque to be set for the actuator 3. The actuator 3 feeds backthe actual value N of its rotation speed to the regulator 1.

In contrast to the control system illustrated in FIG. 1, the controlsystem shown in FIG. 2 also has a decision-maker 5 which receives, asinput variables, the nominal rotation speed N_(nom) and the output valuefrom the regulator 1 (in this case the current value I_(nom)). An output“LOCK” from the decision-maker 5 acts on the amplifier 2 in order tolock the actuator 3 when necessary. In this context, the term “lock” canmean that the actuator 3 is entirely switched off or is just switched toproduce no torque. In the latter case, the load 4 then brakes theactuator 3.

FIG. 3 shows a preferred exemplary embodiment of the decision-maker 5,in the form of a block diagram. The nominal rotation speed N_(nom) actson a model block 10, which produces a modeled rotation speed profilewith respect to time, or has calculated such a profile, and passes thisto its output. The output from the model block 10 and the nominalrotation speed N_(nom) are supplied as input variables to a comparator20. If the input variables to the comparator 20 match, that is to say ifthe instantaneous values of the nominal rotation speed N_(nom) and ofthe modeled motor rotation speed of the model block 10 match, a signalSTAT is set as the output from the comparison 20. In the exemplaryembodiment explained here, the signal STAT is set from a value STAT=0 toa value STAT=1 if the input variables to the comparator 20 match.

The output value I_(nom) from the regulator 1 has the mathematical signremoved from it via a magnitude-forming device 30 and is input, as aninput variable, to a sample and hold register 40 which receives, as afurther input variable, the signal STAT, by means of which it iscontrolled. When the signal changes from STAT=0 to STAT=1, the sampleand hold register 40 stores the value of I_(nom), with the mathematicalsign removed from it, that is applied to its input at this time as avalue I_(s), and passes this to its output.

An adder 45 receives, as input variables, the value of I_(s) which isstored at that time by the sample and hold register 40 and is applied tothe output of the latter. Furthermore, the adder receives as an input avalue ΔI which defines a permissible discrepancy for the value I_(nom).This permissible discrepancy ΔI is preferably an upward discrepancy, sothat the adder 45 obtains a maximum value I_(max) by adding the sampledvalue I_(s) to the discrepancy ΔI, and supplies this as its output.

The output value I_(max) from the adder 45 is compared by a furthercomparator 50 with the output value, from which the magnitude has beenremoved, of the present value of I_(nom). If this instantaneous value,from which the magnitude has been removed, of I_(nom) is greater thanthe maximum value I_(max) an output signal from the comparator 50changes from a value 0 to a value 1. This output signal from thecomparator 50 and the signal STAT from the comparator 20 are input asinput variables into an AND gate 60 which sets the signal LOCK at itsoutput from a value 0 to a value 1 if both the signal STAT and theoutput signal from the comparator 50 have the value 1 at the same time.

The method of operation of the decision-maker 5 can be seen from thegraphs in FIGS. 4a and 4 b, with both FIGS. 4a and 4 b showing anexample when the load on the actuator 3 from the load 4 is low. For thisload example, FIG. 4a shows firstly the profile of I_(nom) and thesignals STAT and LOCK plotted against time. In a corresponding way, FIG.4b shows the rotation speed profile for this example, with respect totime. In this case, FIG. 4b shows, firstly, the profile of the nominalrotation speed N_(nom) and of the model curve MODEL produced in themodel-forming device 10. To assist understanding, FIG. 4b also shows theactual profile of the actual value N of the rotation speed.

From the time T₀ (in this case: t=0) to a time T₁ (in this case, forexample: t=0.02 s), the values of N_(nom) and of the modeled curve MODELmatch (both are equal to zero). In a corresponding way, the signal STATis equal to 1 from T₀ to T₁. Since the value of I_(nom) is approximately0 from T₀ to the time T₁, the output signal from the comparator 50 islikewise 0 so that, overall, the signal LOCK is 0.

From the time T₁ until the time T₂, the values of N_(nom) and of themodel curve MODEL differ, so that the comparator 20 sets the signalSTAT=0. In a corresponding way, the signal LOCK also remains 0.

At the time T₂, the rotation speed reaches an operating valueN_(OPERATION), and the nominal value curve N_(nom) meets the modeledcurve MODEL at this value N_(OPERATION). Since the two values now match,the comparator 20 accordingly sets the signal STAT from 0 to 1. Thevalue of I_(nom) with the mathematical sign removed from it, in thesample and hold register 40 at this time T₂ is stored as I_(s) in thesample and hold register 40, and is supplied to the adder 45. The adder45 also adds the permissible discrepancy ΔI to this stored value I_(s),and passes the sum on as its output I_(max) to the input of thecomparator 50.

From T₂ until the time T₃, the actual value I_(nom) is less than themaximum value I_(max), so that the output value from the comparator 50remains 0 and, in a corresponding way, the output value from the ANDgate 60 remains LOCK=0.

The magnitude of I_(nom) does not exceed the value I_(max) until thetime T₃, so that the output from the comparator 50 changes from 0 to 1.Since the signal STAT is 1 at this time and both input signals to theAND gate 60 are thus one, the output signal LOCK from the AND gate 60likewise has to change to 1. This signal LOCK=1 from the decision-maker5 once again acts on the amplifier 2. On the basis of the signal LOCK=1,the amplifier 2 then sets the current value supplied to the actuator 3to zero, so that the actuator 3 does not produce any torque, and theload 4 slowly brakes the actuator 3 to 0, as can be seen from FIG. 4b.

The decision-maker 5 therefore in each case stores as I_(s) in thesample and hold register 40 that value of I_(nom) which is actuallypresent (with the mathematical sign removed from it) at the time T₂ whenthe operating value N_(OPERATION) is reached, and in each case uses thistogether with the permissible discrepancy ΔI to monitor for the torquebeing exceeded after the time T₂. If the torque is then exceeded, thesignal LOCK=1 is triggered, and the decision-maker 5 stops the actuator3 via the amplifier 2.

FIGS. 5a and 5 b show a further example of a high load situationcorresponding to the illustration in and description relating to FIGS.4a and 4 b, that is to say for the situation where the load 4 in theFIGS. 5 is greater than that in the FIGS. 4. This is particularlyevident in the values for the current I_(nom) which are considerablyhigher in FIG. 5a than in FIG. 4a. Since FIGS. 4 and 5 are intended torelate to the same exemplary embodiment, the profiles of N_(nom) andMODEL in FIGS. 4 and 5 are the same, and accordingly also once againrelate to the time T₂.

In a corresponding manner to that in the above statements relating toFIGS. 4a and 4 b, the signal STAT changes from 1 to 0 at the time T₁,and remains at STAT=0 until the time T₂, at which the value of N_(nom)once again matches the value on the MODEL curve. At this time T₂, theinstantaneous value I_(nom) is stored in the sample and hold register40, with its magnitude removed, as I_(s). If this value I_(s) stored inthe sample and hold register 40 is exceeded, added to the discrepancyΔI, at the time T₃, the signal LOCK is set from 0 to 1, and theamplifier 2 is switched to produce no torque.

It can be seen in particular from the differences between FIGS. 4a and 5a how the invention allows a lower or higher maximum current I_(max)depending on the load situation, only beyond which is the actuator 3switched to produce no torque. In consequence, the switching-offthreshold is adaptively matched to the actual load conditions at the endof the acceleration process, when the operating rotation speedN_(OPERATION) is reached. It is thus possible to identify whether thereis any reason to switch off, essentially independently of the actualload state. The system must not be switched off if the operating statesare permissible.

As can be seen from FIGS. 4 and 5, the operation of the control systemillustrated in FIG. 2 can be subdivided into two load phases I and II.The first load phase I starts with the acceleration of the actuator 3 atthe time T₁ from 0 to the desired rotation speed N_(OPERATION). The loadphase I ends at the time at which the operating rotation speedN_(OPERATION) has been reached, and the acceleration process has thusbeen completed. This condition is satisfied at the time T₂.

The second load phase II therefore starts at the time T₂ and does notend again until the time T₃, when the value I_(max) is exceeded.

Since it is also permissible for the value of I_(nom) to be increased,without this being a reason for switching off, during acceleration tothe operating rotation speed N_(OPERATION) in the load phase I, faultidentification is deactivated in this load phase I and the signal LOCKis set to 0. As soon as the operating rotation speed N_(OPERATION) isreached in the load phase II, the identification of the presence of areason for switching off if the maximum current value I_(max) isexceeded can be activated, so that increased torques can be avoided. Ascan be seen from FIGS. 3-5, the decision-maker 5 requires, as inputvariables, only the nominal rotation speed value N_(nom) and the outputvalue I_(nom) from the regulator 1, which corresponds to the torque, inorder to determine the signal LOCK. Instead of the actual value of therotation speed N, which is shown only for further information purposesin FIGS. 4b and 5 b, the decision-maker 5 uses the modeled motorrotation speed characteristic MODEL for determining the sampled valuesI_(s).

It is immediately evident that, in particular, the time T₂ at which thevalue of MODEL corresponds to the value of N_(nom) can be influenced bythe choice and the presetting of this modeled rotation speedcharacteristic MODEL. The duration of the load phase I can thus beshortened or lengthened by suitable design of the characteristic MODEL.In a further embodiment, the profile of the MODEL curve is in this casepredetermined such that it can be adaptively matched to the respectivesituation rather than being static.

The use of the model profile MODEL instead of a comparison with theactual rotation speed N has the advantage that, if the model profileMODEL is preset in an appropriate manner, it can reliably be assumedthat the system has reached a steady state of the operating rotationspeed N_(OPERATION), and instantaneous increases in the rotation speed(for example in the event of an overshoot) do not corrupt the value.

As can be seen, the time profile of the actual value N can likewise alsobe used instead of the model curve MODEL for the comparison by thecomparator 20 with the nominal value N_(nom). While this would not leadto any significant change in the duration of the load phase I in theprofile at low load shown in FIG. 4b, in the high load case shown inFIG. 5b, the duration of the load phase I would be considerablyshortened to the time between the time T₁ and a time T₂′ at which thevalues of N_(nom) and N match. While, in a corresponding manner, thisdoes not result in any change to the holding value of the current I_(s)in the case shown in the FIGS. 4, the resultant value I_(s)′ at the timeT₂′ in the example in the FIGS. 5 would be somewhat greater than thevalue I_(s) at the time T₂.

When choosing the model characteristic MODEL, care must be taken, inparticular, to ensure that this, at least in principle, corresponds tothe actual profile of the actual value N. However, if, as is preferable,the overshoot actually occurs at high load (see FIG. 5b in the timeperiod between 0.15 and 0.2 seconds), this should not be precipitatedinto the model characteristic MODEL, since the steady state has not yetoccurred at this time. The profile of the model characteristic MODELaccordingly corresponds, in a suitable manner, more to the profile ofthe actual rotation speed N when the load is very low, and this was alsothe situation chosen in the cases in FIGS. 4b and 5 b.

The defined discrepancy ΔI supplied to the adder 45 in FIG. 3 can eitherbe preset as a fixed value or else can be adaptively matched, forexample, to the conditions at that time. In the exemplary embodimentsillustrated in FIGS. 3-5, it is only worthwhile monitoring an upwarddiscrepancy so that the value of ΔI is added to the value of I_(s) inorder to determine the value I_(max). In a corresponding manner, inapplications in which it is intended to monitor a downward discrepancyof the torque in the same way or instead (for example in order toidentify whether the load has been lost), the circuit can be adapted inan appropriate manner as shown in FIG. 3. However, this changes nothingwith regard to the fundamental relationships.

As can be seen from the comparison of FIGS. 4 and 5 for the situationswhere the load differs, the invention allows the value of I_(s) to bematched adaptively to the respective load conditions that are actuallyoccurring during the load phase I. The torque profile of I_(nom) canthen be monitored for undesirable overshoots and/or undershoots withrespect to these actual load conditions in the subsequent load phase II.

In the exemplary embodiment of the application of the control systemillustrated in FIG. 2 to a transport device (for example in aircraft),the area between T₀ and T₁ illustrated in FIGS. 4 and 5 corresponds to aloading phase in which the conveyor belt has packages placed on it whileit is stationary. The actuator 3 is switched on at the time T₁, andaccelerates in the load phase I to the motor operating rotation speedN_(OPERATION). The load phase II following this is continued until theactuator 3 is either switched off manually or automatically when theconveyor belt reaches a desired position, or the signal LOCK signals afault state. In the former case, the conveyor belt can then once againhave items placed on it while it is stationary, so that the illustratedconditions recur successively. In the latter case of a malfunction,steps to rectify the malfunction can be initiated when such amalfunction is identified by the occurrence of the signal LOCK.

What is claimed is:
 1. A method for monitoring a first control value(I_(nom)) for overshooting or undershooting of a threshold value(I_(max)), with the first control value (I_(nom)) being used forcontrolling an apparatus (3); having the following steps: a)determination of the threshold value (I_(max)) from instantaneous value(I_(s)) of the first control value (I_(nom)) when the apparatus (3)reaches a predetermined operating state, and b) monitoring the firstcontrol (I_(nom)) for overshooting or undershooting of the determinedthreshold value (I_(max)) when the apparatus (3) reaches thepredetermined operating state.